One of the most pressing issues in cosmology is whether general relativity
(GR) plus a dark sector is the underlying physical theory or whether a modified
gravity model is needed. Upcoming dark energy experiments designed to probe
dark energy with multiple methods can address this question by comparing the
results of the different methods in constraining dark energy parameters.
Disagreement would signal the breakdown of the assumed model (GR plus dark
energy). We study the power of this consistency test by projecting constraints
in the w_0-w_a plane from the four different techniques of the Dark Energy
Survey in the event that the underlying true model is modified gravity. We find
that the standard technique of looking for overlap has some shortcomings,
propose as an alternative the Multi-dimensional Consistency Test, and introduce
the methodology for projecting whether a given experiment will be able to
distinguish a modified gravity model from GR.

This is a very nicely written paper that explores how well upcoming experiments such as the Dark Energy Survey will be able to distinguish between GR+dark energy and modified gravity.

The basic idea is that different probes of dark energy (supernovae, weak lensing, large scale structure, and clusters) depend differently on the growth of structure, so a disagreement between these methods when analyzed assuming GR could provide evidence that gravity needs to be modified. They conclude that the standard method of checking the overlap of error ellipses in the w0-wa plane is not sufficiently sensitive to distinguish their toy modified gravity model from GR, and go on to develop a more sensitive method using the full multi-parameter likelihood space.

The paper also includes a really nice overview of modified gravity parameterizations and Fisher matrix methodology.

Overall I think their multi-dimensional consistency test is a fundamentally simple but powerful formalism that could be applied to many other types of consistency checks as well.

Joined: 24 Sep 2004Posts: 149Affiliation: University College London (UCL)

Posted: June 26 2010

Yes, I agree this is a nice illustration of a basic but useful idea, and an interesting development of it.

It would be really nice if there could be a visual way of getting across the effectiveness of the multi-dimensional consistency test, that was similarly powerful to Fig 4 (e.g. some projection in n-d which shows up discrepancies??).